Inkjet head and method of ejecting ink using the same

ABSTRACT

Disclosed is an inkjet head and a method of ejecting an ink using the same. An inkjet head according to one embodiment of the present invention may include nozzles each including a ejecting hole through which a solution including a light-emitting element is ejected and pairs of electrodes which are provided around the ejecting holes to face each other and which apply an electrode voltage to the light-emitting element.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2021-0030854, filed on Mar. 9, 2021, the disclosureof which is incorporated herein by reference in its entirety.

BACKGROUND 1. Field of the Invention

The present invention relates to an inkjet head and a method of ejectingan ink using the same, and more specifically, to an inkjet head used ina manufacturing process of a display device and a method of ejecting anink using the same.

2. Discussion of Related Art

Display devices are classified into liquid crystal displays (LCDs),organic light emitting diode (OLED) displays, plasma display panels(PDPs), micro-light emitting diodes (LEDs), quantum nano emitting diode(QNED) displays, and the like according to a light-emitting method.

Among them, the QNED display is a display using a light-emitting elementbased on quantum dots, which are nanometer size ultra-smallsemiconductor particles, and gallium nitride (GaN).

The light-emitting element has a nanorod type having a long stick shapeand an ultra-small size. The QNED is formed by jetting and arranginglight-emitting elements on each of pixels through an inkjet printingprocess.

In a Korean patent publication (Patent Publication No. 10-2019-0137742,“LED ELECTRODE ASSEMBLY AND MANUFACTURING METHOD THEREOF”), a method ofmanufacturing an LED electrode assembly which is capable of preventingelectrode damage and a short circuit which may occur when LED elementsare arranged is disclosed, but it has a problem in that the LED elementhaving a predetermined length in an arrangement process after a jettingoperation is not properly arranged in the jetting and arrangingprocesses due to shape specificity of the light-emitting element.

RELATED ART Patent Document

-   (Patent Document 0001) Korean Patent Publication No. 10-2019-0137742    (Published Date: Dec. 11, 2019)

SUMMARY OF THE INVENTION

The present invention is directed to providing an inkjet head capable ofimproving arrangement accuracy of light-emitting elements in amanufacturing process of a display device and a method of ejecting anink using the same.

The present invention provides an inkjet head in order to solve thetechnical problem. According to an aspect of the present invention,there is provided an inkjet head including nozzles each including aejecting hole through which a solution including a light-emittingelement is ejected and pairs of electrodes which are provided around theejecting hole to face each other and which apply an electrode voltage tothe light-emitting element.

The inkjet head may further include an insulating layer interposedbetween end portions of the nozzles and the electrodes.

The nozzles may be disposed to form one or more rows, and the electrodesmay include first electrodes provided in a row along one end portions ofthe plurality of adjacent nozzles and second electrodes provided in arow along the other end portions of the nozzles in a direction oppositeto a direction of the first electrodes.

The first electrodes may be disposed a predetermined distance apart fromthe second electrodes in one direction.

The inkjet head may further include a first piezoelectric element whichchanges an internal pressure of a reservoir filled with the solution, anactuator which changes a piezoelectric element voltage applied to thefirst piezoelectric element to eject the solution through the ejectinghole, and a controller which controls a magnitude of an electrodevoltage applied to the electrodes, wherein the controller may controlthe magnitude of the electrode voltage independently of thepiezoelectric element voltage based on the piezoelectric elementvoltage.

The inkjet head may further include a second piezoelectric elementinterposed between the end portions of the nozzles and the electrodes.

The present invention provides a method of ejecting an ink in order tosolve the technical problem.

According to an aspect of the present invention, there is provided amethod of ejecting an ink comprising a first arrangement operation ofapplying an electrode voltage to a ejecting hole of a nozzle throughwhich a solution including a light-emitting element is supplied so as toarrange one end portion and the other end portion of the light-emittingelement in an arbitrary direction, a jetting operation of jetting thesolution on a substrate on which a first substrate electrode and asecond substrate electrode are disposed to be spaced apart from eachother, and a second arrangement operation of applying power to thesubstrate so that the one end portion of the light-emitting element isdisposed on the first substrate electrode and the other end portion isdisposed on the second substrate electrode.

Before a jetting process in the jetting operation is performed, thefirst arrangement operation and the jetting process are concurrentlyperformable.

In the first arrangement operation, an electrode voltage having amagnitude which is different from a magnitude of a piezoelectric elementvoltage for ejecting the solution through the ejecting hole may beapplied.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent to those of ordinary skill in theart by describing exemplary embodiments thereof in detail with referenceto the accompanying drawings, in which:

FIG. 1 is a front view illustrating an inkjet head and a substrateaccording to one embodiment of the present invention;

FIG. 2 is an enlarged view illustrating portion A in FIG. 1;

FIG. 3A is a schematic view illustrating a moving state of a solutionejected from a conventional inkjet head;

FIG. 3B is a schematic view illustrating a moving state of a solutionejected from an inkjet head according to one embodiment of the presentinvention;

FIG. 4 is a bottom view illustrating the inkjet head according to oneembodiment of the present invention;

FIG. 5A is a schematic perspective view illustrating a substrate onwhich a first electrode and a second electrode according to oneembodiment of the present invention are mounted;

FIG. 5B is a plan view illustrating the substrate on whichlight-emitting elements in an arranged state is provided according toone embodiment of the present invention;

FIGS. 6A and 6B are views illustrating the light-emitting elementaccording to one embodiment of the present invention; and

FIG. 7 is a flowchart illustrating a method of ejecting an ink accordingto one embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.However, the technical spirit of the present invention is not limited tothe embodiments which will be described in this specification and may berealized with different forms. Further, the embodiments introduced inthis specification are provided so that the disclosed content isthorough and complete and the spirit of the present invention issufficiently conveyed to those skilled in the art.

In the present specification, when a certain component is described asbeing present on another component, it means that the component may bedirectly disposed on another component, or a third component may beinterposed therebetween. In addition, in the accompanying drawings,shapes and sizes are exaggerated to effectively describe the technicalcontent.

In addition, although the terms “first,” “second,” “third,” and the likeare used herein to describe various elements in the various embodimentsof the present specification, these elements should not be limited bythese terms. These terms are only used to distinguish a certain elementfrom another element. Accordingly, an element described as a firstelement in any one embodiment may be described as a second element inanother embodiment. The embodiments described and illustrated in thisspecification include complementary embodiments thereof. In addition,the term “and/or” is used to include at least any one of elements listedtherebefore and thereafter.

The singular forms are intended to include the plural forms, unless thecontext clearly indicates otherwise. In addition, the terms “comprise,”“include,” or the like specify the presence of features, numbers, steps,operations, elements, or combinations thereof which are described in thespecification, but do not preclude the presence or addition of one ormore other features, numbers, steps, operations, elements, orcombinations thereof. In addition, in this specification, the term“connect” is used to include both indirect and direct connection of aplurality of elements.

In addition, in the following description, when it is determined thatdetailed descriptions of related well-known functions or configurationsunnecessarily obscure the gist of the present invention, the detaileddescriptions thereof will be omitted.

FIG. 1 is a front view illustrating an inkjet head 10 and a substrate 30according to one embodiment of the present invention, FIG. 2 is anenlarged view illustrating portion A in FIG. 1, FIG. 3A is a schematicview illustrating a moving state of solutions 21 and 22 ejected from aconventional inkjet head 10′, FIG. 3B is a schematic view illustrating amoving state of solutions 21 and 22 ejected from the inkjet head 10according to one embodiment of the present invention, FIG. 4 is a bottomview illustrating the inkjet head 10 according to one embodiment of thepresent invention, FIG. 5A is a schematic perspective view illustratingthe substrate 30 on which a first electrode 210 and a second electrode220 according to one embodiment of the present invention are mounted,FIG. 5B is a plan view illustrating the substrate 30 on whichlight-emitting elements 22 in an arranged state are provided accordingto one embodiment of the present invention, and FIGS. 6A and 6B areviews illustrating the light-emitting element 22 according to oneembodiment of the present invention.

Hereinafter, components of the inkjet head 10 according to oneembodiment of the present invention will be described in detail.

Referring to FIGS. 1 to 6B, the inkjet head 10 according to oneembodiment of the present invention may be a device configured toprovide the solutions 21 and 22 including the light-emitting elements 22to the substrate 30. The inkjet head 10 may include nozzles 100 andelectrodes 200 and may further include insulating layers 300, firstpiezoelectric elements 400, an actuator 500, a controller 600, andsecond piezoelectric elements 700.

Referring back to FIGS. 1 to 4, the nozzles 100 may include ejectingholes 110. The ejecting holes 110 may eject the solutions 21 and 22including the light-emitting elements 22.

The nozzles 100 may be disposed to form one or more rows.

A reservoir 120 may accommodate the solutions 21 and 22. One end of thereservoir 120 may communicate with the ejecting holes 110.

Referring back to FIGS. 1 to 3B, the solutions 21 and 22 may include adispersion solvent 21. Preferably, the dispersion solvent 212 may be anyone or more from the group consisting of acetone, water, alcohol, ortoluene, but is not limited thereto, and any solvent may be used withoutlimitation as long as the light-emitting elements 22 are not physicallyor chemically affected and the volatilization performance thereof ishigh.

Referring back to FIGS. 1 to 6B, the light-emitting elements 22 may berotated in the dispersion solvent 21 by electrostatic attractive forcesof the first electrode 210 and the second electrode 220 in an arbitrarydirection. The light-emitting elements 22 may be jetted after a firstarrangement is performed so that the light-emitting elements 22 arearranged on a first electrode 210 and a second electrode 220 to faceeach other before the light-emitting elements 22 are jetted.

The light-emitting elements 22 may be formed so that a first conductivesemiconductor layer 22 a and a second conductive semiconductor layer 22c are formed on both end portions of an active layer 22 b in alongitudinal direction. Referring to FIG. 6A, the light-emitting element22 may include the first conductive semiconductor layer 22 a, the activelayer 22 b formed on the first conductive semiconductor layer 22 a, andthe second conductive semiconductor layer 22 c formed on the activelayer 22 b. Referring to FIG. 6B, an insulating layer 22 d may be formedon an outer circumference of the light-emitting element 22 to surroundthe first conductive semiconductor layer 22 a, the active layer 22 b,and the second conductive semiconductor layer 22 c.

Any one of the first conductive semiconductor layer 22 a and the secondconductive semiconductor layer 22 c may be an n-type semiconductorlayer, and the other may be a p-type semiconductor layer.

According to one embodiment, when the first conductive semiconductorlayer 22 a is the n-type semiconductor layer, at least one or more maybe selected from semiconductor materials having a composition formula ofIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, 0≤x+y≤1), for example, InAlGaN,GaN, AlGaN, InGaN, AlN, or InN, as the first conductive semiconductorlayer 22 a, and a first conductive dopant may be doped. The firstconductive dopant may be Si, Ge, or Sn, but is not limited thereto. Whenthe second conductive semiconductor layer is the p-type semiconductorlayer, at least one or more may be selected from semiconductor materialshaving a composition formula of In_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1,0≤x+y≤1), for example, InAlGaN, GaN, AlGaN, InGaN, AlN, or InN, as thep-type semiconductor layer, and a second conductive dopant may be doped.The second conductive dopant may be Mg but is not limited thereto.

The active layer 22 b may be interposed between the first conductivesemiconductor layer 22 a and the second conductive semiconductor layer22 c and may have a single or multi quantum well structure. A generalactive layer 22 b included in a general light-emitting element 22 usedin a lighting, a display, and the like may be used as the active layer22 b. When an electric field due to a predetermined voltage or more isapplied to both ends of the light-emitting elements 22, electron-holepairs are coupled in the active layer 22 b so that the light-emittingelements 22 may emit light.

The insulating layer 22 d may be provided to surround all or some of thefirst conductive semiconductor layer 22 a, the active layer 22 b, andthe second conductive semiconductor layer 22 c. The insulating layer 22d may be formed of a transparent material. The insulating layer 22 d maybe at least one or more among SiO₂, Si₃N₄, Al₂O₃, and TiO₂ but is notlimited thereto.

The insulating layer 22 d may prevent a short circuit between thelight-emitting elements 22 randomly positioned in the dispersion solvent21.

The light-emitting element 22 may have a rod shape. An aspect ratio ofthe light-emitting element 22 may be in the range of 1.2 to 100,preferably 1.2 to 50, more preferably 1.5 to 20, and more preferably 1.5to 10.

The light-emitting element 22 may have a nanoscale diameter and/orlength.

Referring back to FIGS. 1 to 4, pairs of the electrodes 200 may beformed on the ejecting holes 110 to face each other. The electrodes 200according to one embodiment may be provided at front ends of theejecting holes 110. The electrodes 200 may apply an electrode voltage tothe light-emitting elements 22. The electrodes 200 may include firstelectrodes 210 and second electrodes 220. The electrodes 200 may applyan alternating current voltage.

An arbitrary potential difference may occur between the first electrodes210 and the second electrodes 220. The first electrodes 210 according toone embodiment may be provided in one row along one end portions of theplurality of adjacent nozzles 100.

The first electrodes 210 may be disposed a predetermined distance fromthe second electrodes 220. The first electrodes 210 may be provided tobe disposed in parallel to face a first substrate electrode 31. Thefirst electrodes 210 and the second electrodes 220 may be disposed toface the first substrate electrode 31 and the second substrate electrode32.

The first electrodes 210, along with the second electrodes 220, may beprovided to be disposed to surround the front ends of the ejecting holes110.

The first electrodes 210 may be formed of at least one or more metalsamong aluminum, titanium, indium, gold, and silver or at least one ormore transparent materials among indium tin oxide (ITO), ZnO:Al, and acarbon nano tube (CNT)-conductive polymer composite. When the firstelectrode 210 is formed of two or more materials, the materials may beformed to be stacked on each other.

The second electrodes 220 may be provided to face the first electrodes210 and spaced the predetermined distance apart from the firstelectrodes 210. The second electrodes 220 according to one embodimentmay be provided in a row at the other end portions of the nozzles 100.The second electrodes 220 may be provided to be disposed in parallel toface a second substrate electrode 32.

The second electrodes 220 may be formed of at least one or more metalsamong aluminum, titanium, indium, gold, and silver or at least one ormore transparent materials among indium tin oxide (ITO), ZnO:Al, and acarbon nano tube (CNT)-conductive polymer composite. The secondelectrode 220 may be formed of a material which is the same as ordifferent from a material of the first electrode 210.

The first electrodes 210 and the second electrodes 220 according to oneembodiment may be arranged to correspond with each other in any onedirection according to arrangement positions of the first substrateelectrode 31 and the second substrate electrode 32 disposed on thesubstrate 30. According to one embodiment, the first electrodes 210 maybe provided to face the second electrodes 220 in a Y-axis direction. Thefirst electrodes 210 may be connected to a voltage source, a resistor,and the second electrodes 220 in series.

Referring back to FIGS. 1 and 3B, in a first nozzle 100, an electrodevoltage may be provided so that the first electrode 210 is arrangedparallel to the first substrate electrode 31, and the second electrode220 is arranged parallel to the second substrate electrode 32, in anX-axis direction, respectively, and in a second nozzle 100, an electrodevoltage may be provided so that the first electrode 210 is arrangedparallel to the second substrate electrode 32 and the second electrode220 is arranged parallel to the first substrate electrode 31.

Referring back to FIGS. 1 to 4, the insulating layer 300 may prevent thenozzle 100 from being short-circuited with the electrode 200. Theinsulating layer 300 may be interposed between an end portion of thenozzle 100 and the electrode 200. The insulating layer 300 may insulatethe electrode 200 from the end portion of the nozzle 100. The insulatinglayer 300 may prevent an electrical short circuit between the endportion of the nozzle and the first electrode or the second electrodeand damage thereof due to the solvent or conductive impurities providedin a process of jetting the solutions 21 and 22 including thelight-emitting elements 22. The insulating layer 300 may be formed of atleast any one among SiO₂, Si₃N₄, SiN_(x), Al₂O₃, HFO₂, Y₂O₃, and TiO₂but is not limited thereto. According to one embodiment, the insulatinglayer 300 may be formed of silicon nitride (SiN_(x)).

Referring back to FIGS. 1 and 2, the actuator 500, which will bedescribed below, may drive the first piezoelectric elements 400 togenerate a pressure against the solutions 21 and 22. The firstpiezoelectric elements 400 may change an internal pressure of thereservoir 120. The reservoir 120 may be filled with the solutions 21 and22.

Referring back to FIG. 1, the actuator 500 may apply a piezoelectricelement voltage having an arbitrary value to the first piezoelectricelements 400. The actuator 500 may change the arbitrary piezoelectricelement voltage to control the solutions 21 and 22 to be ejected throughthe ejecting holes 110.

When the actuator 500 drives the first piezoelectric elements 400, aninternal volume of the reservoir 120 may be reduced, and thus thesolutions 21 and 22 may be ejected through the ejecting holes 110 due toa change in pressure of the reservoir 120.

Referring back to FIG. 1, the controller 600 may adjust a magnitude ofan electrode voltage applied to the electrode. The controller 600 mayrequire information of the actuator 500. The controller 600 may receivea value of a piezoelectric element voltage from the actuator 500. Thecontroller 600 may arbitrarily control the magnitude of the electrodevoltage applied to the electrodes 200 independently of the value of thepiezoelectric element voltage.

Referring back to FIGS. 1 to 3B, the second piezoelectric element 700may be interposed between the end portion of the nozzle 100 and theelectrode 200. The second piezoelectric element 700 may provide aejecting pressure with the same phase as the first piezoelectric element400.

The second piezoelectric elements 700 may be synchronized with the firstpiezoelectric elements 400 to form a predetermined acoustic vibration.The second piezoelectric elements 700 may add wave energy to wave energyapplied to the ejecting holes 110 by the first piezoelectric elements400 to increase a ejecting force of the solutions 21 and 22 at theejecting holes 110.

The second piezoelectric elements 700 according to one embodiment may beselectively formed along with the insulating layer 300. The secondpiezoelectric element 700 according to another embodiment may beprovided to be interposed between an insulating layer 300 and theelectrode 200.

Referring back to FIGS. 1, 2, 5A, and 5B, the substrate 30 may includethe first substrate electrode 31 and the second substrate electrode 32.The first substrate electrode 31 may be disposed a predetermineddistance apart from the second substrate electrode 32 on the substratein one direction. The first substrate electrode 31 according to oneembodiment may be provided to face the second substrate electrode 32 inthe Y-axis direction.

The substrate 30 may be formed of a rigid or flexible material. Thesubstrate 30 may be at least one among a glass substrate, a crystalsubstrate, a sapphire substrate, a plastic substrate, or a flexiblesubstrate such as a polymer film, and may be a substrate on which anelectrode may be formed. According to one embodiment, the substrate 30may be formed of a transparent material but is not limited thereto. Inaddition, the substrate 30 may also be formed of a translucent, opaque,or reflective material.

Hereinafter, a method of ejecting an ink using the inkjet head 10according to one embodiment of the present invention will be describedaccording to time series.

FIG. 7 is a flowchart illustrating the method of ejecting an inkaccording to one embodiment of the present invention.

Referring to FIG. 7, the method of ejecting an ink according to oneembodiment of the present invention may provide the light-emittingelements on the substrate in order from operations of performing a firstarrangement before the solutions including the light-emitting elementare jetted, applying the solutions including the light-emittingelements, performing a second arrangement of the light-emittingelements, and removing the solvent.

The method of ejecting an ink according to one embodiment of the presentinvention may include a first arrangement operation (S10), a jettingoperation (S20), and a second arrangement operation (S30)

In the first arrangement operation S10, one end portions and the otherend portions of the light-emitting elements may be arranged in anarbitrary direction by applying an electrode voltage to the ejectinghole of the nozzle through which the solutions including thelight-emitting elements are supplied.

Before a jetting process of the jetting operation, the first arrangementoperation S10 and the jetting process may be concurrently performed.

In the first arrangement operation S10, an electrode voltage having amagnitude different from that of a piezoelectric element voltage forejecting the solutions through the ejecting hole may be applied.

In the first arrangement operation S10, the light-emitting elements maybe rotated in an arbitrary direction by applying an electrostaticattractive force using dipole characteristics of the light-emittingelements before the solutions including the light-emitting elements areejected from the inkjet head in the jetting operation.

In the jetting operation S20, the light-emitting elements may be jettedand applied on the substrate by ejecting the solutions including thelight-emitting elements from the inkjet head. In this case, the firstsubstrate electrode and the second substrate electrode may be disposedto be spaced apart from each other on the substrate.

In the second arrangement operation S30, one end portions of thelight-emitting elements may be arranged to be disposed on the firstsubstrate electrode and the other end portions of the light-emittingelements may be arranged to be disposed on the second substrateelectrode by applying power to the substrate.

According to the embodiments of the present invention, there is anadvantage of improving an arrangement yield on a substrate by applyingan electrode voltage to an electrode to rotate a light-emitting elementbefore a jetting process is performed.

According to one embodiment of the present invention, since theelectrodes are provided at the ejecting holes, the light-emittingelements are primarily arranged by applying the electrode voltageapplied before and during ejecting, and thus there are advantages inthat arrangement characteristics of the light-emitting elements can beimproved and a product yield of a display device can be improved throughan elaborate arrangement.

According to another embodiment of the present invention, a controllercan control a magnitude of an electrode voltage independently of apiezoelectric element voltage, and there is an advantage in that thevertical falling performance of light-emitting elements can be improvedby controlling the electrode voltage to have the same phase and the samemagnitude as those of the piezoelectric element voltage.

Although the present invention has been described in detail through theexemplary embodiments, the scope of the present invention is not limitedto the detailed description but should be interpreted based on theappended claims. In addition, those skilled in the art will understandthat many modifications and variations are possible without departingfrom the scope of the present invention.

What is claimed is:
 1. An inkjet head comprising: nozzles each includinga ejecting hole through which a solution including a light-emittingelement is ejected; and pairs of electrodes which are provided aroundthe ejecting holes to face each other and which apply an electrodevoltage to the light-emitting element.
 2. The inkjet head of claim 1,further comprising an insulating layer interposed between end portionsof the nozzles and the electrodes.
 3. The inkjet head of claim 1,wherein: the nozzles are disposed to form one or more rows; and theelectrodes include first electrodes provided in a row along one endportions of the plurality of adjacent nozzles and second electrodesprovided in a row along the other end portions of the nozzles in adirection opposite to a direction of the first electrodes.
 4. The inkjethead of claim 1, wherein the first electrode is disposed a predetermineddistance apart from the second electrode in one direction.
 5. The inkjethead of claim 1, further comprising: a first piezoelectric element whichchanges an internal pressure of a reservoir filled with the solution; anactuator which changes a piezoelectric element voltage applied to thefirst piezoelectric element to eject the solution through the ejectinghole; and a controller which controls a magnitude of an electrodevoltage applied to the electrode, wherein the controller controls themagnitude of the electrode voltage independently of the piezoelectricelement voltage based on the piezoelectric element voltage.
 6. Theinkjet head of claim 5, further comprising a second piezoelectricelement interposed between the end portions of the nozzles and theelectrodes.
 7. A method of ejecting an ink comprising: a firstarrangement operation of applying an electrode voltage to a ejectinghole of a nozzle through which a solution including a light-emittingelement is supplied so as to arrange one end portion and the other endportion of the light-emitting element in an arbitrary direction; ajetting operation of jetting the solution on a substrate on which afirst substrate electrode and a second substrate electrode are disposedto be spaced apart from each other; and a second arrangement operationof applying power to the substrate so that the one end portion of thelight-emitting element is disposed on the first substrate electrode andthe other end portion is disposed on the second substrate electrode. 8.The method of claim 7, wherein, before a jetting process in the jettingoperation is performed, the first arrangement operation and the jettingprocess are concurrently performable.
 9. The method of claim 7, wherein,in the first arrangement operation, an electrode voltage having amagnitude which is different from a magnitude of a piezoelectric elementvoltage for ejecting the solution through the ejecting hole is applied.